A self-diagnosis method for hot film airflow mass microsensor has been developed for the vehicle air intake. Based on
the theory of heat transfer and airflow mass rate measurement for internal combustion engines, a hot film airflow mass
microsensor with self-diagnosis capability is designed. It is composed of a heat sensing unit, a temperature sensing unit
using a Heraeus silicon, a signal processor, a converters, a heater, a heating controller and a computer. The temperature
sensing unit is split into a heater upstream temperature sensing resistor and a heater downstream temperature sensing
resistor according to the air intake flow direction. From both theory and experiments, the relation between the heat
transfer rate of the heater and the airflow mass rate at the air intake are deduced under the working conditions of a certain
engine, and the temperature distribution rules in the heater surface, heater upstream and heater downstream are obtained.
These relations are regarded as a reference model for the self-diagnosis in the microsensor. Finally, the failure of the
microsensor can be detected by comparing the real-time measurement model with the reference model. Thus, this
method can not only measure mass airflow rates in real time, but also inspect diagnosis faults of the heat sensing unit and
the temperature sensing unit automatically.